Brief Answer: I am not very concerned... Detailed Answer: Foreign body such a a small piece of bone causes issues unless they are below the lower end of esophagus (food pipe). Chances of serious complications are exceedingly low when its out of your food pipe into the stomach. Further when its within the food pipe it always causes symptoms of something stuck and heart burns. Since you are completely asymptomatic, I guess there is nothing to be worried about. If you are concerned about new symptoms happening, then you need X-rays or CT scan of chest and abdomen. That should locate the position of bone and its course through the gut. Hope this helped you. Regards

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